As chlorofluorocarbon (CFC), a refrigerant used for a refrigerator, an air-conditioner or the like, has been known as a source material damaging an ozone layer of the stratosphere, researches on a substitute refrigerant are being actively conducted.
The substitute refrigerant for CFC/HCFC is desired to be environment-friendly as well as to have excellent thermodynamical and chemicophysical characteristics. That is, the substitute refrigerant should have a high energy efficiency, a zero ozone layer disintegration index, a low global warming index, no toxic character and incombustibility.
There are a few refrigerants which have no toxicity and no combustibility and are not CFC among methane-based and ethane-based halocarbon compounds: R22, R23, R134a, R123, R124 and R125. Of them, R22, R123 and R124, which are HCFC, are under regulation, and in case of R23, even though it is a kind of HFC, its thermodynamical property is not so good as to be utilized as a refrigerant.
HFC pure refrigerants usable as a substitute refrigerant among halocarbon are very limited. Thus, mixed refrigerants have been studied and developed as substitute refrigerants by mixing two or three pure materials at a suitable composition ratio to make up for shortcomings of the pure materials and thus obtain a good environment index.
R134a, R152a or cyclopropane (RC270) can substitute R12 which has been widely used for the home-use refrigerators and automobile air-conditioners. An HFC mixed refrigerant such as R404A and R507 is being taken into account as a substitute refrigerant of R502 mainly used as a low temperature refrigerant. Meanwhile, HFC mixed refrigerants including R32 are considered as substitute refrigerants of R22 used for a heat pump and various air-conditioning devices. Researches are under way for those substitute refrigerants.
The CFC includes R11 (trichloromonogluoromethane), R12 (dichlorodifluoromethane), R113 and the like, of which R12 largely used as a refrigerant for a refrigerator is one of regulation-subject materials as being a source material causing an ozone layer reduction and generating a global warming effect. Thus, currently, R134a is put to a practical use as a substitute refrigerant of R12.
As a representative example of HCF, R134a exhibits a zero ozone depletion potential, incombustibility and physical properties similar to R12, and is widely used as such.
However, with all those advantages, R134a is hardly combined with refrigerant oil currently used for a refrigerating system of R12 due to its peculiar chemical and electrical properties. Therefore, a refrigerant oil suitable for the refrigerant R134a is in need of development. Especially, necessity of a refrigerant oil usable for a reciprocating compressor for compressing the refrigerant R134a comes to the front.
FIG. 1 shows a construction of a general refrigerating cycle.
As shown in FIG. 1, a currently used refrigerating cycle includes: an evaporator 2 for performing a cooling operation as a low temperature and low pressure liquid refrigerant is evaporated; a compressor 4 for compressing the low temperature and low pressure gaseous refrigerant discharged from the evaporator 2 to a high temperature and high pressure gaseous refrigerant; a condenser 6 for changing the high temperature and high pressure gaseous refrigerant discharged from the compressor 4 to a high temperature and high pressure liquid refrigerant; and a capillary tube 8 for decompressing the refrigerant discharged from the condenser 6 so as to be easily evaporated and transferring it to the evaporator 2.
The refrigerant used for the refrigerating system is R134a, and a refrigerant oil used for the compressor 4 needs to have such physical and chemical characteristics that it is well harmonized with the refrigerant R134a.
That is, the refrigerant oil of the refrigerating system should have characteristics that it protects a oil film sufficiently even though the refrigerant is dissolved, it is sufficiently stable thermally and chemically so as not to react in spite of being in contact with a refrigerant or an organic material metal, etc. at a high temperature or at a low temperature, and it has a high level of thermal stability so as not to generate a carbon sludge or not to be oxidized at a high temperature part of the compressor.
In order to satisfy those characteristics, characters of the lubricant, such as a kinematic viscosity, a pour point, a density, a total acid number, a water content or the like, work as critical factors.
Therefore, if the refrigerant oil used for the refrigerating system is not harmonized with the refrigerant, oil circulation is deteriorated to degrade a heat transfer performance of the refrigerating system and a lubrication performance, resulting in that frictional portions of each motional part are abraded and thus each part is damaged. Then, the performance of the refrigerating system is deteriorated.